Data storage device defining track trajectory to reduce ac track squeeze

ABSTRACT

A data storage device is disclosed comprising a head actuated over a disk comprising servo data for defining a plurality of data tracks, wherein each data track comprises a plurality of data segments. First data is written to data segments of a first data track, and second data is written to data segments of a second data track. After writing the second data, the first data is read at multiple off-track offsets of the first data track to measure an average off-track read capability (OTRC) of the first data track. A cross-track profile is generated for a first data segment of the first data track, and at least part of the cross-track profile is correlated with the measured average OTRC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/456,381 filed on Jun. 28, 2019, which is hereby incorporated byreference in its entirety.

BACKGROUND

Data storage devices such as disk drives comprise a disk and a headconnected to a distal end of an actuator arm which is rotated about apivot by a voice coil motor (VCM) to position the head radially over thedisk. The disk comprises a plurality of radially spaced, concentrictracks for recording user data sectors and servo sectors. The servosectors comprise head positioning information (e.g., a track address)which is read by the head and processed by a servo control system tocontrol the actuator arm as it seeks from track to track.

A disk drive typically comprises a plurality of disks each having a topand bottom surface accessed by a respective head. That is, the VCMtypically rotates a number of actuator arms about a pivot in order tosimultaneously position a number of heads over respective disk surfacesbased on servo data recorded on each disk surface. FIG. 1 shows a priorart disk format 2 as comprising a number of servo tracks 4 defined byservo sectors 6 ₀-6 _(N) recorded around the circumference of each servotrack. Each servo sector 6 _(i) comprises a preamble 8 for storing aperiodic pattern, which allows proper gain adjustment and timingsynchronization of the read signal, and a sync mark 10 for storing aspecial pattern used to symbol synchronize to a servo data field 12. Theservo data field 12 stores coarse head positioning information, such asa servo track address, used to position the head over a target datatrack during a seek operation. Each servo sector 6 _(i) furthercomprises groups of servo bursts 14 (e.g., N and Q servo bursts), whichare recorded with a predetermined phase relative to one another andrelative to the servo track centerlines. The phase based servo bursts 14provide fine head position information used for centerline trackingwhile accessing a data track during write/read operations. A positionerror signal (PES) is generated by reading the servo bursts 14, whereinthe PES represents a measured position of the head relative to acenterline of a target servo track. A servo controller processes the PESto generate a control signal applied to a head actuator (e.g., a voicecoil motor) in order to actuate the head radially over the disk in adirection that reduces the PES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servotracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a head actuated over a disk.

FIG. 2B is a flow diagram according to an embodiment wherein a tracktrajectory is generated for a target data track based on a measuredtrack pitch of a data segment.

FIG. 2C shows an embodiment wherein the data tracks are written with anoverlap in a technique referred to as shingled recording.

FIG. 2D shows an embodiment wherein the track trajectory for a targetdata track is generated by measuring a delta (A) between a measuredtrack pitch and a target track pitch for multiple data segments aroundthe target data track.

FIGS. 2E and 2F show an embodiment wherein the delta (A) between themeasured track pitch and a target track pitch for a data segment may benegative (meaning the measured track pitch is greater than the targettrack pitch).

FIGS. 3A and 3B show an embodiment wherein a cross-track profile of eachdata segment of the target data track is generated and used to measurethe track pitch at each data segment.

FIGS. 4A-4E show an embodiment wherein the quality metric for generatingthe cross-track profile is an error rate of the data segment.

FIGS. 5A and 5B show an embodiment for generating the track trajectoryof a target data track.

FIGS. 6A-6F show an embodiment wherein the quality metric for generatingthe cross-track profile is a signa-to-noise (SNR) of the data segment.

FIG. 7A shows an embodiment wherein turning point of the cross-trackprofile is estimated by curve fitting the quality metrics measured attwo off-track offsets of a data segment.

FIG. 7B shows an embodiment wherein different curve fitting functionsare used to estimate the turning point of the cross-track profiledepending on the circumferential location of the data segment around thetarget data track.

FIG. 8 shows an embodiment wherein the track trajectory of a target datatrack is measured as part of a write operation when writing user data tothe target data track.

FIG. 9 shows an embodiment wherein the off-track deviations of the tracktrajectories propagate from track to track.

FIG. 10 shows a closed loop control system for controlling a VCM whileaccessing a data track, wherein repeatable runout (RRO) values are usedto define the track trajectory of the target data track.

FIGS. 11A and 11B show an embodiment wherein for a radial band of datatracks PES RRO values may be used when the data tracks are non-shinglewritten, and data sector squeeze RRO values may be used when the datatracks are shingle written.

FIG. 12A shows an embodiment wherein a disk surface may comprise anumber of zones, wherein each zone comprises a radial band of datatracks.

FIG. 12B is a flow diagram according to an embodiment wherein a zone maybe non-shingle written using PES RRO and later shingle written usingdata sector squeeze RRO.

FIG. 13A shows an embodiment wherein the logical block addressing (LBA)of a zone of data tracks may be dynamically configured into anon-shingled or shingled data track format.

FIG. 13B is a flow diagram according to an embodiment wherein PES RROmay be generated for at least two zones of data tracks during amanufacturing procedure, and data sector squeeze RRO may be generatedfor the zones while the disk drive is deployed in the field.

FIG. 13C is a flow diagram according to an embodiment wherein whenduring a write operation, the data sector squeeze RRO values may begenerated on-the-fly for the target data track.

FIG. 14A shows an embodiment wherein first PES RRO is used to generate afirst track trajectory used to write a data track and second PES RRO isused to generate a second track trajectory used to read the data track.

FIG. 14B shows an embodiment wherein data sector squeeze RRO is used togenerate a track trajectory used to read a first data track, and used towrite a second adjacent (shingle written) data track.

DETAILED DESCRIPTION

FIG. 2A shows a data storage device in the form of a disk drivecomprising a head 16 actuated over a disk 18 comprising servo data fordefining a plurality of data tracks, wherein each data track comprises aplurality of data segments. The disk drive further comprises controlcircuitry 20 configured to execute the flow diagram of FIG. 2B, whereinfirst data is written to a first data segment of a first data track(block 22), and second data is written to a second data segment of asecond data track (block 24) such as shown in FIG. 2C. After writing thesecond data, a quality metric for at least two off-track offsets of thefirst data segment is measured (block 26), and a track pitch isestimated between the first data segment and the second data segmentbased on the quality metrics (block 28). A track trajectory is generatedfor the second data segment based on the estimated track pitch (block30), and third data is written to the second data segment based on thetrack trajectory (block 32) such as shown in FIG. 2D or FIG. 2F.

In the embodiment of FIG. 2A, the disk 18 comprises a plurality of servosectors 34 ₁-34 _(N) that define a plurality of servo tracks 36, whereindata tracks are defined relative to the servo tracks 36 at the same ordifferent radial density. The control circuitry 20 processes a readsignal 38 emanating from the head 16 to demodulate the servo sectors andgenerate a position error signal (PES) representing an error between theactual position of the head and a target position relative to a targettrack. A servo control system in the control circuitry 20 filters thePES using a suitable compensation filter to generate a control signal 40applied to a VCM 42 which rotates an actuator arm 44 about a pivot inorder to actuate the head radially over the disk surface in a directionthat reduces the PES. In one embodiment, the head 16 may be actuatedover the disk 18 based on the PES using one or more secondary actuators,for example, a microactuator that actuates a suspension coupling a headslider to the actuator arm 44, or a microactuator that actuates the headslider relative to the suspension (e.g., using a thermal actuator,piezoelectric actuator, etc.). The servo sectors 34 ₁-34 _(N) maycomprise any suitable head position information, such as a track addressfor coarse positioning and servo bursts for fine positioning. The servobursts may comprise any suitable pattern, such as an amplitude basedservo pattern or a phase based servo pattern (FIG. 1).

In one embodiment, the data tracks are written in a consecutive order(e.g., from an outer diameter toward an inner diameter) with apredetermined overlap, such as shown in FIG. 2D or FIG. 2F, in atechnique referred to as shingled recording. Conventionally the shingleddata tracks are written with sufficient spacing (track pitch) so as tocompensate for the worst case AC track squeeze that may occur around thecircumference of a data track. However, compensating for the worst caseAC track squeeze may lead to a larger than necessary track pitch for asignificant number of data segments (e.g., data sectors) around thecircumference of each data track. That is, adding a margin into thetarget track pitch in order to compensate for the worst case AC tracksqueeze in shingled recording reduces the maximum capacity of the diskdrive. Accordingly, in one embodiment the track pitch for each datasegment around the circumference of a data track is estimated in orderto generate a track trajectory, wherein the track trajectory is used towrite each data segment so as to substantially achieve a target trackpitch around the circumference of the data track (i.e., reduce theamplitude of the AC track squeeze). This enables a significant reductionin the margin conventionally added to the target track pitch in shingledrecording, thereby increasing the radial density of the data tracks andoverall capacity of the disk drive.

Referring again to FIG. 2C or FIG. 2E, in one embodiment theuncompensated track pitch for a data segment of a first data track isestimated by writing a first test pattern to the first data segment, andthen shingle writing a second data segment of a second data track(adjacent the first data track) based on an uncompensated tracktrajectory (e.g., no repeatable runout (RRO) compensation). Theuncompensated track pitch is then estimated, for example, using anembodiment described below, thereby generating a delta (A) between theuncompensated track pitch and a target track pitch of the first datasegment (positive as shown in FIG. 2C or negative as shown in FIG. 2E).In one embodiment, this measured delta (Δ) is converted into a tracktrajectory (e.g., in the form of RRO compensation values) for writingdata to the second data segment, thereby achieving the target trackpitch for the first data segment as shown in FIG. 2D or FIG. 2F. Thisprocess is then repeated for the second data segment in order togenerate a track trajectory used to write the next, adjacent datasegment of the next adjacent data track, and so on, thereby propagatingthe track trajectories of shingled data tracks across at least part ofthe disk surface.

Any suitable technique may be employed to estimate the track pitch of anuncompensated data segment such as shown in FIG. 2C. In one embodiment,after writing the second, overlapping data segment, a quality metric ismeasured for at least two off-track offsets of the first data segment.That is, the head 16 is positioned at an off-track offset (relative tothe uncompensated target track center) in order to measure a qualitymetric of the resulting read signal. As shown in FIGS. 3A and 3B, thequality metric changes (increases/decreases) as the off-track offsetincreases and the quality of the resulting read signal decreases. Anysuitable quality metric may be measured, such as a sector error rate(SER) which represents a number of bits (or symbols) in error afterprocessing the read signal with a suitable sequence detector (e.g., aViterbi detector). In this embodiment, the quality metric (e.g., numberof errors) increases as the off-track offset increases as shown in FIG.3A due to the lower quality of the read signal. Another example qualitymetric may include a signal-to-noise ratio (SNR) metric measured for theread signal, wherein the SNR metric decreases as the off-track offsetincreases as shown in FIG. 3B. In one embodiment, the width of thecross-track profile such as shown in FIG. 3A may be defined relative towhen the measured quality metrics exceed a threshold.

In one embodiment, the target track pitch of the shingled data tracksmay be determined by generating a similar cross-track profile as shownin FIG. 3A wherein the measured quality metric may be a sector failurerate (SFR) which represents a number of times a data sector fails a readoperation at an off-track offset. That is at each off-track offset, thecontrol circuitry 20 attempts to recover each data sector of the datatrack (e.g., using full Viterbi plus LDPC decoding of a reach channel),wherein the SFR metric may represent a number of times each sector failsout of a predetermined number of attempts to read each data sector(e.g., over multiple disk revolutions). As the off-track offsetincreases, the SFR metric for each data sector increases due to thelower quality of the read signal. This embodiment is understood withreference to FIG. 4A which shows the AC track squeeze of the datasectors around a full data track while shingle writing two adjacent datatracks at a narrowing track pitch. At each track pitch, an SFRcross-track profile is generated such as shown in FIG. 3A for each datasector of the first uncompensated data track (wherein in FIG. 4A, themiddle of the darker shade represents the bottom of the SFR cross-trackprofile). The track pitch is incrementally reduced and the average widthof the average SFR cross-track profile around the first data track(referred to as the average off-track read capability (OTRC)) ismeasured and correlated with track pitch as shown in FIG. 4C. A targettrack pitch (TP) is then selected as the track pitch that corresponds toa target average OTRC as shown in FIG. 4C. In one embodiment, a targettrack pitch may be determined for each of a plurality of zones definedacross the radius of the disk by performing the above measurements fortwo adjacent data tracks within each zone. That is, the data tracks ofeach zone are shingle written at a target track pitch corresponding to atarget average OTRC as described above.

In one embodiment, measuring an SFR metric for each data sector in eachdata track of a zone in order to estimate the uncompensated track pitchof each data sector may be prohibitively time consuming due to themultiple disk revolutions needed to measure the SFR metric at eachoff-track offset. Accordingly in one embodiment, when estimating theuncompensated track pitch of each data sector of a data track, an SERmetric may be generated at each off-track offset. In one embodiment, theSER metric for a data sector may be generated over a single revolutionof the disk at each off-track offset, or generated over multiplerevolutions of the disk at each off-track offset and the resulting SERmetrics averaged in order to filter out noise. In one embodiment, thenumber of revolutions needed to generate an accurate SER metric issignificantly less than the number of revolutions needed to generate anaccurate SFR metric, and therefore the SER metric enables a fasterestimation of the track pitch at each uncompensated data sector ascompared to generating an SFR metric for each data sector.

FIG. 4B shows a measured SER metric for each data sector of the firstuncompensated data track at each of the narrowing track pitches (i.e.,the SER metric for each data sector corresponding to the SFR metricshown in FIG. 4A). In one embodiment, the SER metric of each data sectoris correlated with the SFR metric to enable the track pitch of eachuncompensated data sector to be estimated much faster as compared togenerating an SFR metric for each data sector (due to the fewer numberof revolutions needed to generate the SER metric).

This embodiment is understood with reference to FIG. 4E which shows anumber of SER cross-track profile bottoms (or turning points in FIG. 3A)measured for a number of data sectors at each track pitch of FIG. 4B. Asthe track pitch is narrowed, the bottom of the SER cross-track profilewill shift by an off-track offset toward the non-overlapping side of thedata track (toward the top of the first data track shown in FIG. 2C). Anexample of a shifting bottom of a cross-track profile is described belowwith reference to FIG. 7A. An OTRC is also measured for each data sectorat each track pitch and correlated with the off-track offset where thebottom of the SER cross-track profile occurs as shown in FIG. 4E. Inthis manner, the SER cross-track profile bottom may be estimated for anygiven data sector of any given data track within a zone, and used toestimate the corresponding OTRC using FIG. 4E and corresponding trackpitch using FIG. 4C. Once the estimated track pitch of an uncompensateddata sector is estimated, the delta (Δ) between the estimated trackpitch and the target track pitch may be generated (as shown in FIG. 4C)and correlated with an off-track offset that will achieve the targettrack pitch as shown in FIG. 4D. Each off-track offset shown in FIG. 4Dcorresponds to the off-track offset where the bottom of the average SFRcross-track profile occurs. That is, in one embodiment the bottom of theaverage SFR cross-track profile will shift toward the non-overlappingside of the data track as the track pitch decreases. Accordingly, foreach narrowing track pitch and corresponding delta (Δ) from the targettrack pitch, a corresponding off-track offset that achieves the targettrack pitch may be generated for each uncompensated data sector usingthe relationship of FIG. 4D, thereby generating a track trajectory forwriting the adjacent, overlapping data track. That is, the adjacent,overlapping data track (second data track of FIG. 2D or FIG. 2F) iswritten along the track trajectory to achieve a substantially constant(target) track pitch for the data sectors in the overlapped data track(first data track in FIG. 2D or FIG. 2F).

To summarize the above process, the three trends shown in FIGS. 4C, 4Dand 4E are first established by generating the SFR and SER cross-trackprofiles for each data sector of a target data track in a target zone(after having been shingle written by an adjacent data track). Once thethree trends are established, only the SER cross-track profile needs tobe generated (or estimated in an embodiment described below) for eachuncompensated data sector in each data track of the zone. The bottom ofthe SER cross-track profile for each data sector may then be transformedinto a corresponding value (off-track offset) of the track trajectoryused to write the adjacent data track. An example of this embodiment isshown in FIG. 5A, wherein the top graph 46 represents the estimated OTRCof each uncompensated data sector of a target data track as convertedusing Trend A (FIG. 4E), and the bottom graph 48 represents theestimated track pitch for each uncompensated data sector as convertedusing Trend B (FIG. 4C). FIG. 5B shows the resulting track trajectory 50(off-track offsets) as converted using Trend C (FIG. 4D) for writing theadjacent data track (the second graph 52 in FIG. 5B is the off-trackoffset of the SER cross-track profile bottom for each data sector). Inan embodiment described in greater detail below, the track trajectoryfor writing the adjacent data track is also saved and used as the tracktrajectory for reading the target data track (the first data track inFIG. 2D or FIG. 2F).

Any suitable quality metric may be measured to generate the cross-trackprofile (such as shown in FIG. 3A or FIG. 3B) and the correspondingtrack trajectory for each data segment of a data track. FIGS. 6A-6F showan embodiment wherein the quality metric measured to generate thecross-track profile includes a signal-to-noise ratio (SNR) metric of theread signal. In the embodiment of FIG. 6A, the SNR metric is generatedby writing a first frequency test pattern (e.g., a 2T pattern) to a datatrack N−1, writing a second frequency test pattern (e.g., a 5T pattern)to a target data track N, and writing a third frequency test pattern(e.g., a 3T pattern) to a data track N+1. The SNR metric for a datasegment of the target data track N is then generated by reading the datasegment and processing the resulting read signal to compute:

SNR=[Amp_(5T)]/sqrt([Amp_(4.5T)]²+[Amp_(2T)]²+[Amp_(3T)]²)

where Amp_(2T) represents the amplitude of the read signal at the 2Tfrequency component, Amp_(3T) represents the amplitude of the readsignal at the 3T frequency component, Amp_(4.5T) represents theamplitude of the read signal at the 4.5T frequency component (narrowband noise), and Amp_(5T) represents the amplitude of the read signal atthe 5T frequency component. The above frequency components may beextracted from the read signal in any suitable manner, such as with adigital pass-band filter or by computing a Fourier transform at eachfrequency. FIG. 6B shows example SNR cross-track profiles for a numberof the data segments of a target data track, and for incrementallynarrower track pitches. FIG. 6B illustrates in this embodiment how thepeak of the cross track profile shifts (by an off-track offset) as thetrack pitch decreases. This shift in the peak of the cross-track profileis correlated with the measured OTRC for each data segment as shown inFIG. 6F which is similar to correlating the shift of the bottom of theSER cross-track profile with the measured OTRC as shown in theembodiment of FIG. 4E. Similar to the embodiment described above, oncethe three trends (FIGS. 6D, 6E and 6F) are generated for a zone, thetrack trajectories for the data tracks of the zone may be generated bymeasuring the off-track offset of the peak in the SNR cross-trackprofile for each data segment, and then transforming the measurementinto a corresponding off-track offset of the track trajectory.

In one embodiment, the cross-track profile of a data segment (such asshown in FIG. 3A or 3B) may be generated using brute force by measuringa quality metric at a number of off-track offsets across the target datatrack. In another embodiment, the quality metric may be measured atfewer off-track offsets, and then the measured quality metrics curvefitted to a cross-track profile based on predetermined, nominalcross-track profiles (or functions representing the nominal cross-trackprofiles). FIG. 7A shows an example of this embodiment, wherein thequality metric may be measured at two off-track offsets (offset A andB), and then curve fitting the resulting two quality metrics to generatea corresponding cross-track profile. In this embodiment, the cross-trackprofile may be generated over two disk revolutions to measure the twoquality metrics as the two off-track offsets A and B. In anotherembodiment, the head 16 may comprise two radially offset read elementssuch that the two quality metrics at the two off-track offsets A and Bmay be measured over a single disk revolution.

In one embodiment, the predetermined, nominal cross-track profiles usedfor curve fitting the quality metrics may vary depending on thecircumferential location of the data segments around a data track.Accordingly in an embodiment shown in FIG. 7B, the circumference of thedisk may be divided into multiple arcs, wherein predetermined, nominalcross track profiles may be generated for each arc and used to curve fitthe measured quality metrics of a data segment within each arc.

In the embodiments described above, the turning point of the cross-trackprofile (e.g., SER bottom or SNR peak) is correlated with the OTRC ofthe data segment. In other embodiments, a different parameter of thecross-track profile may be correlated with the OTRC of the data segment,such as correlating the width of the cross-track profile with the OTRC.

In one embodiment, the track trajectory for each data track may begenerated during a manufacturing procedure of the disk drive before thedisk drive is deployed in the field. In another embodiment, the tracktrajectory for each data track may be generated after the disk drive hasbeen deployed in the field as part of normal write operations. Anexample of this embodiment is shown in the table of FIG. 8, wherein thefirst column of the table represents a step of write operations, themiddle columns represent a write/read operation of a data track, and thelast column indicates when the track trajectory (read/write) aregenerated for each data track. The steps of the write operation are asfollows:

Step 1: write test pattern to data track 0;Step 2; write dummy pattern to data track 1 overlapping data track 0 ata target track pitch;Step 3: read the test pattern from the data sectors in data track 0 inorder to measure the cross track profiles and generate the correspondingtrack trajectory (write trajectory for track 1 and read trajectory fortrack 0);Step 4: write test pattern to data track 1;Step 5: write dummy pattern to data track 2 overlapping data track 1 atthe target track pitch;Step 6: read the test pattern from the data sectors in data track 1 inorder to measure the cross track profiles and generate the correspondingtrack trajectory (write trajectory for track 2 and read trajectory fortrack 1);Step 7: write customer data (user data) to data track 0 using the writetrajectory generated at Step 3;Steps 8+: repeat the above steps for the remaining data tracks.

In one embodiment, the off-track offsets of a track trajectory generatedfor data track N are propagated when generating the track trajectory forthe next adjacent data track N+1. This embodiment is illustrated in FIG.9 which shows example track trajectories generated for a zone comprising100 data tracks and the corresponding increase in the AC amplitude ofthe track trajectories due to the propagating off-track offsets. In oneembodiment, the maximum AC amplitude of the track trajectories may belimited so as to suppress a divergence condition by introducing a smallscaling factor ε to each off-track offset when generating a tracktrajectory:

Trk_Trj[N+1]=Trk_Trj[N]_(DC)+TP+(1−ε)*Trk_Trj[N] _(AC)

where Trk_Trj[N+1] represents the write track trajectory generated fordata track N+1, Trk_Trj[N]_(DC) represents the DC component of the writetrack trajectory generated for data track N, TP represents the targettrack pitch, and Trk_Trj[N]_(AC) represents the AC component of thewrite track trajectory generated by processing data track N. Anysuitable scaling factor ε may be employed, such as (ε=0.05), and in oneembodiment the scaling factor may be adaptively adjusted based on theamplitude of the AC component of the write track trajectories generatedfor the data tracks (e.g., adaptively increase the scaling factor εproportional to the amplitude of the AC component).

In one embodiment, the calibration procedure for generating the threetrends described above with reference to FIGS. 4C-4E or FIGS. 6D-6F maybe repeated by rewriting the target and adjacent data track at eachnarrowing track pitch. The resulting three trends generated for eachiteration may then be averaged to generate a final, more accurate threetrends. In another embodiment, the procedure for measuring thecross-track profile of the data sectors of a target track may berepeated (by rewriting the target and adjacent data tracks) and theresulting track trajectories averaged. In yet another embodiment, whenrewriting the adjacent data track, the previously generated tracktrajectory may be used to rewrite the adjacent data track. That is, thetrack trajectory may be incrementally adjusted for each rewriteoperation so that the track trajectory may converge to a more accuratefinal trajectory. In one embodiment, rewriting the data tracks in orderto average or adapt to the final track trajectory helps filter outnon-repeatable runout (NRRO) from the cross-track profile measurement.

FIG. 10 shows a closed loop control system according to an embodimentfor controlling the VCM 42 so that the head 16 follows the tracktrajectory during write/read operations. A position 54 of the head ismeasured and subtracted from a reference position 56 to generate aposition error signal (PES) 58. The PES 58 is filtered using anysuitable compensation algorithm 60 to generate the control signal 40applied to the VCM 42. The reference position 56 represents thewrite/read track trajectory described above and is generated by addingrepeatable runout (RRO) values 62 to a target position 64, wherein theRRO values 62 correspond to the AC component (off-track offsets) of thetrack trajectory generated for the target data track as described above.In one embodiment, the off-track offsets (e.g., FIG. 4D) for generatingthe track trajectory correspond to an output response of the VCM 42 inthe closed loop control system of FIG. 10. Accordingly, in oneembodiment in order to generate the RRO values 62 the off-track offsets(e.g., FIG. 4D) are transformed into values at the input of thecompensator 60 by filtering the off-track offsets with a sensitivityfunction of the closed loop control system. In one embodiment, theoff-track offsets of the track trajectory may also be phase shifted(e.g., using an interpolation filter) so as to align with the samplephase and sample rate of the servo sectors 34 ₁-34 _(N).

In one embodiment, the disk 18 is divided into a plurality of zones suchas shown in FIG. 12A, wherein each zone comprises a plurality of datatracks. FIG. 12B is a flow diagram according to an embodiment whereinPES RRO values are generated based on the servo data in a first zone(block 62), and data sector squeeze RRO values are generated based ondata segments in the first zone (block 64). First data is written to thedata tracks of the first zone according to a non-shingled data trackformat for the first zone based on the PES RRO values (block 66). Thefirst data is overwritten with second data according to a shingled datatrack format based on the data sector squeeze RRO values (block 68).

FIG. 11A shows an example of a number of data tracks of a first zonewritten according to a non-shingled data track format based on PES RROvalues, and FIG. 11B shows a number of data tracks of the first zonewritten according to a shingled data track format based on data sectorsqueeze RRO values. The PES RRO values in FIG. 11A are generated basedon the PES 58 of the closed loop control system of FIG. 10 using anywell known technique. The data sector squeeze RRO values in FIG. 11B aregenerated based on the estimated track pitch of each data sector aftershingle writing a second data track over a first data track as describedabove. In the example of FIG. 11A, the width (track pitch) of the datatracks equals the width of the servo tracks. However in otherembodiments, the track pitch of a non-shingled data track format may begreater than or less than the track pitch of the servo tracks.

In one embodiment, each zone in the example of FIG. 12A may be formattedand accessed according to either a non-shingled data track format or ashingled data track format. When formatted according to a non-shingleddata track format, the RRO values 62 in FIG. 10 used to define the tracktrajectory (reference position 56) are the PES RRO values such as shownin FIG. 11A. When formatted according to a shingled data track format,the RRO values 62 in FIG. 10 used to define the track trajectory(reference position 56) are the data sector squeeze RRO values such asshown in FIG. 11B. In one embodiment shown in FIG. 13A, the controlcircuitry may dynamically configure the formatting of each zone into anon-shingled data track format or a shingled data track format. In oneembodiment, the capacity of the shingled data track format is largerthan the non-shingled data track format due to the increase in thenumber of data tracks (decrease in track pitch) that is achieved due tooverlapping the data tracks as shown in FIG. 11B.

In an embodiment shown in FIG. 13A, logical block addresses (LBAs) aremapped to the physical data sectors of a zone depending on how the zoneif formatted. When the zone is formatted according to a first data trackformat based on the PES RRO (e.g., a non-shingled data track format),LBAs 0-J are mapped to the physical data sectors of the zone, and whenthe zone is formatted according to a second data track format based onthe data sector squeeze RRO (e.g., a shingled data track format), LBAsN-M are mapped to the physical data sectors of the zone (where thenumber of LBAs of the shingled data track format is significantlygreater than the number of LBAs of the non-shingled data track format).In one embodiment, dynamically adjusting the LBA address range isimplemented using a prior art protocol referred to as Dynamic HybridShingled Magnetic Recording (DHSMR) which enables the host to access adisk drive that is implementing a dynamic adjustment of the LBA addressrange.

FIG. 13B is a flow diagram according to an embodiment wherein during amanufacturing procedure PES RRO is generated for a plurality of thezones (such as shown in FIG. 12A) and the zones formatted according tofirst data track format (block 70). The disk drive is then deployed inthe field, for example, shipped to a designated customer (block 72).When the disk drive is first powered on, the control circuitrycommunicates to the host an available LBA address range whichcorresponds to the zones initially formatted at block 70 (which in oneembodiment may be all of the zones on the disk). The disk drive serviceshost write commands by writing data to the formatted zones, such aswriting data to a first zone using the corresponding PES RRO (block 74),or writing data to a second zone using the corresponding PES RRO (block76). During an idle time of the disk drive, the control circuitrygenerates data sector squeeze RRO values for at least two of the zones(block 78) and generates a second data track format for the zones basedon the data sector squeeze RRO as described above. Once the data squeezeRRO has been generated and the second data track format generated forthe corresponding zone, the control circuitry communicates to the hostthe availability of an extended LBA address range for the zone such asshown in FIG. 13A. When the control circuitry receives a command fromthe host to convert a zone to the second data track format (block 80),the control circuitry begins writing data to the corresponding zoneusing the data sector squeeze RRO values. In one embodiment, the controlcircuitry may receive a command from the host to convert a SMR zone backinto the first data track format, in which case the control circuitrybegins writing data to the reformatted zone using the PES RRO values.

In one embodiment, a host may transmit a command at block 80 of FIG. 13Bto convert a zone into the second data track format before the controlcircuitry finishes generating the data sector squeeze RRO values for thezone. In this embodiment, when a write command is received from the hostto write data to a data track of the zone, the control circuitry mayexecute the write command by generating the data sector squeeze RROvalues for the data track and then writing the data to the first datatrack (e.g., as described above with reference to FIG. 8). In oneembodiment, the control circuitry may communicate a status of a zone tothe host, including a “cold” status meaning that no data sector squeezeRRO values have been generated for the zone, a “learning” status meaningthat at least some (but not all) of the data sector squeeze RRO valueshave been generated for the zone, or a “hot” status meaning that all ofthe data sector squeeze RRO values have been generated for the zone. Inone embodiment, the host may convert a zone into the second data trackformat even though the zone may be in the “cold” or “learning” mode.When a write command is directed to a “cold” zone, the host will expectthe execution time to increase (throughput to decrease) since the datasector squeeze RRO values are generated on-the-fly during the writeoperation. When a write command is directed to a “learning” zone, thehost will expect the execution time may increase depending on whetherthe write command is directed to data tracks of the zone with or withoutpre-generated data sector squeeze RRO values.

FIG. 13C shows an example of this embodiment, wherein when a writecommand is received to write data to a target data track (block 71), thecurrent data track format for the target data track is checked (block73). When the target data track is formatted based on the PES RRO, thedata is written to the target data track using the PES RRO (block 75).When the target data track is formatted based on the data sector squeezeRRO, and the data sector squeeze RRO values have not been generated(block 77), the data sector squeeze RRO values are generated on-the-flyas part of the write operation (block 79). Once the data sector squeezeRRO values have been generated (or if they were previously generated),the data is written to the target data track using the data squeeze RROvalues (block 81).

In one embodiment, the PES RRO values and the data sector squeeze RROvalues are stored in a non-volatile memory so they may be used duringwrite/read operations by the closed loop control system such as shown inFIG. 10. In one embodiment, either or both of the RRO values may bewritten in a wedge RRO field of each servo sector. Example techniquesfor storing RRO values in a wedge RRO field are disclosed in U.S. Pat.No. 6,657,810 entitled “DISK DRIVE EMPLOYING SEPARATE READ AND WRITEREPEATABLE RUNOUT ESTIMATED VALUES FOR A HEAD HAVING A READ ELEMENTOFFSET FROM A WRITE ELEMENT” and U.S. Pat. No. 8,693,134 entitled“ALTERNATING WEDGE REPEATABLE RUNOUT (WRRO) PATTERN” the disclosures ofwhich are incorporated herein by reference. In another embodiment, oneor both of the RRO values may be stored in a non-volatile semiconductormemory, such as a Flash memory. In yet another embodiment, the PES RROvalues may be stored in a wedge RRO field of the servo sectors, and thedata sector squeeze RRO values may be stored in a dedicated area of eachSMR zone (e.g., at the beginning of each SMR zone). When accessing anSMR zone, the data sector squeeze RRO values may be read from the disk(from the SMR zone) into a non-volatile or volatile semiconductor memory(e.g., a dynamic random access memory (DRAM)) and then used duringwrite/read operations.

FIG. 14A shows an embodiment wherein the head 16 may comprise a writeelement 84 that is radially offset 86 from a read element 88. Whenwriting data to data track 90 based on a non-SMR data track format, thewrite element 84 is positioned over data track 90 based on the servoinformation read by the read element 88 (i.e., based on the servosectors of data track 92). Accordingly, the PES RRO values used to writedata track 90 are generated at the radial location of the read element88 due to the radial offset 86 between the write element 84 and the readelement 88. When reading data track 90, the read element 88 is poisonedover data track 90 as shown in FIG. 14A, and the corresponding PES RROvalues 94 generated for data track 90 are used during the read operation(e.g., by the closed loop control system of FIG. 10).

FIG. 14B shows an embodiment wherein when writing data to data track 96based on a SMR data track format, the data sector squeeze RRO values 98that were generated for adjacent data track 100 (as described above) areused during the write operation (e.g., by the closed loop control systemof FIG. 10). When reading data track 100, the read element 88 ispositioned over data track 100 as shown in FIG. 14B, and the data sectorsqueeze RRO values 98 that were generated for data track 100 are usedduring the write operation. Accordingly in this embodiment, first datamay be read from a first data track 100 based on a track trajectorydefined by the data sector squeeze RRO values 98, and second data may bewritten to a second, adjacent data track 96 based on the same tracktrajectory defined by the same data sector squeeze RRO values 98.

In the embodiments described above, the data sector squeeze RRO valuesmay be generated at any suitable resolution around a data track. In oneembodiment, a data sector squeeze RRO value may be generated for eachdata sector, or a data sector squeeze RRO value may be generated for apredetermined number of consecutive data sectors. In yet anotherembodiment, multiple data sector squeeze RRO values may be generated foreach data sector. That is, the quality metric (e.g., SER) that ismeasured to define the cross-track profile such as shown in FIG. 3A maycorrespond to a single data sector, multiple data sectors, or part of adata sector.

In one embodiment, when accessing an SMR data track the RRO values 62 ofthe closed loop servo system such as shown in FIG. 10 may be updated ata sample rate that is higher than the servo sector 34 ₁-34 _(N) samplerate. That is, in one embodiment the data sector squeeze RRO values maybe generated at a higher resolution than the servo sector 34 ₁-34 _(N)sample rate, and the higher resolution RRO values used to update theclosed loop servo control system so as to further reduce the AC tracksqueeze around the data track.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a data storage controller, orcertain operations described above may be performed by a read channeland others by a data storage controller. In one embodiment, the readchannel and data storage controller are implemented as separateintegrated circuits, and in an alternative embodiment they arefabricated into a single integrated circuit or system on a chip (SOC).In addition, the control circuitry may include a suitable preamp circuitimplemented as a separate integrated circuit, integrated into the readchannel or data storage controller circuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In another embodiment, the instructions are stored on the diskand read into a volatile semiconductor memory when the disk drive ispowered on. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry. In someembodiments, at least some of the flow diagram blocks may be implementedusing analog circuitry (e.g., analog comparators, timers, etc.), and inother embodiments at least some of the blocks may be implemented usingdigital circuitry or a combination of analog/digital circuitry.

In various embodiments, a disk drive may include a magnetic disk drive,an optical disk drive, a hybrid disk drive, etc. In addition, someembodiments may include electronic devices such as computing devices,data server devices, media content storage devices, etc. that comprisethe storage media and/or control circuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device comprising: a diskcomprising servo data for defining a plurality of data tracks, whereineach data track comprises a plurality of data segments; a head actuatedover the disk; and control circuitry configured to: write first data todata segments of a first data track; write second data to data segmentsof a second data track; after writing the second data, read the firstdata at multiple off-track offsets of the first data track to measure anaverage off-track read capability (OTRC) of the first data track;generate a cross-track profile for a first data segment of the firstdata track; and correlate at least part of the cross-track profile withthe measured average OTRC.
 2. The data storage device as recited inclaim 1, wherein the second data track at least partially overlaps thefirst data track.
 3. The data storage device as recited in claim 1,wherein the control circuitry is further configured to: generate a tracktrajectory for a third data track based on the correlation of thecross-track profile with the measured average OTRC; and write third datato the data segments of the third data track based on the tracktrajectory.
 4. The data storage device as recited in claim 3, whereinthe control circuitry is further configured to generate the tracktrajectory for the third data track based on at least part of across-track profile of the third data track.
 5. The data storage deviceas recited in claim 4, wherein the control circuitry is furtherconfigured to generate the track trajectory for the third data trackbased on a turning point of the cross-track profile of the third datatrack.
 6. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to: measure the average OTRC ofthe first data track for each of multiple track pitches of the firstdata track; generate the cross-track profile for the first data segmentof the first data track at each track pitch; and correlate at least partof each cross-track profile with the measured average OTRC at each trackpitch.
 7. The data storage device as recited in claim 6, wherein thecontrol circuitry is further configured to generate a track trajectoryto achieve a target track pitch for a third data track.
 8. The datastorage device as recited in claim 1, wherein the cross-track profile isgenerated based on a quality metric measured when reading the first datasegment at multiple off-track offsets.
 9. The data storage device asrecited in claim 8, wherein the quality metric comprises an error rateof the first data segment.
 10. The data storage device as recited inclaim 8, wherein: the first data consists of a first periodic patternconsisting of a first frequency of transitions; the second data consistsof a second periodic pattern consisting of a second frequency oftransitions; and the quality metric comprises a signal-to-noise (SNR)measurement.
 11. The data storage device as recited in claim 1, whereinthe control circuitry is further configured to generate the average OTRCof the first data track based on a sector failure rate of the first datatrack.
 12. A data storage device comprising: a disk comprising servodata for defining a plurality of data tracks, wherein each data trackcomprises a plurality of data segments; a head actuated over the disk;and control circuitry configured to: write first data to data segmentsof a first data track; write second data to data segments of a seconddata track; after writing the second data, read the first data atmultiple off-track offsets of the first data track to measure an averageoff-track read capability (OTRC) of the first data track; generate atrack trajectory for a third data track based on the measured averageOTRC; and write third data to the data segments of the third data trackbased on the track trajectory.
 13. The data storage device as recited inclaim 12, wherein the second data track at least partially overlaps thefirst data track.
 14. The data storage device as recited in claim 12,wherein the control circuitry is further configured to generate thetrack trajectory for the third data track based on at least part of across-track profile of the third data track.
 15. The data storage deviceas recited in claim 14, wherein the control circuitry is furtherconfigured to generate the track trajectory for the third data trackbased on a turning point of the cross-track profile of the third datatrack.
 16. The data storage device as recited in claim 12, wherein thecontrol circuitry is further configured to: measure the average OTRC ofthe first data track for each of multiple track pitches of the firstdata track; and generate the track trajectory for the third data trackbased on the measured average OTRC of the first data track for each ofthe multiple track pitches of the first data track.
 17. The data storagedevice as recited in claim 16, wherein the control circuitry is furtherconfigured to generate the track trajectory to achieve a target trackpitch for the third data track.
 18. The data storage device as recitedin claim 14, wherein the cross-track profile is generated based on aquality metric measured when reading a first data segment from the thirddata track at multiple off-track offsets.
 19. The data storage device asrecited in claim 18, wherein the quality metric comprises an error rateof the first data segment.
 20. A data storage device comprising: a diskcomprising servo data for defining a plurality of data tracks, whereineach data track comprises a plurality of data segments; a head actuatedover the disk; and a means for generating a track trajectory for a firstdata track, wherein the track trajectory is used to write data to thedata segments of the first data track.